The invention relates to apparatus for forming articles, such as containers, from a web of plastic material and more particularly, to a drive mechanism for moving the web through the apparatus.
Machines for forming articles, such as containers, from a thermoplastic web are well known. These machines usually have the web of material in the form of a roll at one end of the machine. The web is drawn through the sections of the machine in intermittent steps by an indexing drive that operates conveyor guide chains which grip the edges of the web. In the first section of the machine the web is heated until it softens. As the web passes into the next section of the machine, upper and lower dies are brought into contact with it by a forming press so as to mold it into the desired shape. In some cases the press also has a blade which cuts the formed container from the rest of the web; such a device is shown in U.S. Pat. No. 3,561,057 to Robert Butzko. However, there may also be a separate trim or trimming press as shown in U.S. Pat. No. 3,647,335 issued to Fred Brown, Jr. and assigned to the assignee of the present invention. After the container is cut from the web it is stacked at one location while the excess web is directed into a waste bin.
The forming press with its molding or forming dies it typically driven from a main shaft that also drives the trim press and, through intermediate provisions, the guide chain, so that all of the parts of the machine act in the proper sequence. Various cams are located on the main shaft and are used to impart a reciprocating motion to push rods that operate linkages connected to the forming and trim presses. With respect to machines with separate forming and trim presses, the reciprocating push rods can be connected to separate toggle linkages that bring about an opening and closing of the dies.
In the forming press of the machine described in U.S. Pat. No. 3,647,335 to Brown, two separate push rods are connected to the cam shaft and each drives a separate set of toggle linkages, one for the lower die and one for the upper die. Each toggle linkage set has two pairs of members with ends pivotally connected to each other and centrally tied together by an intermediate linkage. The other ends of the toggle linkages are connected to the press frame and one of the dies, respectively.
In U.S. Pat. No. 3,647,335 to Fred Brown, Jr. there is a continuous conveyor chain on each side of the web, which chains are provided with gripping members that grasp the edges of the web. The chains are each entrained about sprockets located at the ends of the machine. Shafts attached to the sprockets contact gears that mesh with gears on a cross shaft connecting them. A commercial crossover cam index is supplied with motive force by a sprocket and chain drive mounted on the main shaft and in turn produces intermittent drive for the cross shaft.
In another patent issued to Fred Brown, Jr. and assigned to the assignee of the present invention, i.e. U.S. Pat. No. 3,659,993, there is shown apparatus for forming containers from a web in which a pin chain for guiding the web, a forming press, a printing press, and a blanking press are all driven from one power shaft. The power shaft is connected to a chain and sprocket drive by means of a jaw clutch. The sprocket drive is moved by the apparatus motor and the jaw clutch is operated by a pneumatic cylinder. Caliper brakes, which operate on disks mounted on the power shaft, are also provided on the power shaft. In the event of an emergency, the apparatus can be quickly stopped by operating the pneumatic cylinder to open the jaw clutch and by operating the brakes.
Since the machines set forth herein are heavily constructed and each press and the chain drive are operated from the main shaft, it can be difficult to stop the chain drive for the web in the event of an emergency merely by disconnecting the main shaft from the motor and applying a brake. Also, it is highly desirable that the chain drive be automatically disconnected if it is subjected to a tension overload, such as might occur if an implement, for example, becomes caught in the conveying chains. Additionally, it can be desirable to stop the chain drive without stopping the presses and other apparatus attached to the main shaft.